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SHA-224 (Secure Hash Algorithm 224-bit) is a cryptographic hash function developed by the U.S. National Security Agency (NSA) and published by the National Institute of Standards and Technology (NIST) as part of the SHA-2 family. Like other members of the SHA-2 family, SHA-224 generates a fixed-size hash value (message digest) from input data of arbitrary length. In the case of SHA-224, the hash value is 224 bits long.
The main difference between SHA-224 and other SHA-2 hash functions, such as SHA-256, SHA-384, and SHA-512, is the length of the generated hash value. SHA-224 was designed to provide cryptographic security comparable to SHA-256, but with a smaller output size, which can be useful in resource-constrained applications or where a shorter hash is required.
The SHA-224 algorithm begins with preprocessing the input message, which includes padding and length addition. The padding ensures that the message length is a multiple of 512 bits. The length addition represents the original message length and is used to prevent length extension attacks.
SHA-224 operates on 512-bit blocks of data and uses 64 rounding constants. The internal state of the hash function consists of eight 32-bit words. The initial values of these words are defined by the standard and play a crucial role in ensuring the cryptographic strength of the algorithm. SHA-224 subjects each block of data to a series of nonlinear operations, including bit shifts, logical operations (AND, OR, XOR), and addition modulo 2^32. These operations scramble the data and create an avalanche effect, in which a small change in the input data leads to a significant change in the output hash value.
SHA-224 is commonly used for data integrity verification, digital signatures, password storage, and other security-related tasks. Although SHA-224 is not as widely used as SHA-256, it is still considered secure enough for many applications. However, with advances in cryptanalysis, it is recommended to use newer and stronger hash functions, such as SHA-3, where possible.